(a) Field of the Invention
The invention concerns an auxiliary device on devices for rolling up weblike material to form rolls so as to preserve the quality of the paper and to improve the winding quality, and also concerns a process of rolling up weblike material. The device and process according to the invention are particularly well suited for the processing of pressure-sensitive material webs. In particular, webs of pressure-sensitive chemically reactive carbon paper can be processed by means of them to form rolls in proper condition.
The quality of winding of rolls of weblike material affects the possiblity of subsequent processing. Various factors are decisive in evaluating the winding quality of a roll:
The layer pressure between the layers of paper generated by the winding traction; the residual tension in the interior of the roll, in connection with which it is to be remembered that part of the winding tension is reduced by the layer pressure of the outer layers; and the winding tension, which depends on the propulsive power of the winding shaft, the pressure of application of the roll to be wound to the roll core or sleeve, and the pressure of any pressure roll employed.
An effort is exerted on the one hand to wind rolls which are as hard as possible, since if the core in particular is wound too loosely, core layers can be displaced laterally outward and the web to be unwound subsequently is difficult to control in the lateral guide. On the other hand, sensitive web materials such as coated papers the coating of which contains pressure-sensitive microcapsules do not allow of high winding tension, since the layer pressure in the interior may not exceed specific values; otherwise the pressure results in premature damage to the capsules which lowers the quality of the material for its proper use. If the tension is too high, local overelongations leading to so-called tension grooves may also occur. These deformations of the paper web represent an impairment of the quality of the paper and also make the paper unusable.
Improvement in the quality of winding by application of the state-of-the-art pressure rolls with hard surfaces is not possible in the case of pressure-sensitive web materials. This quality is prematurely destroyed by the pressure applied in the case of coatings containing pressure-sensitive microcapsules. It is necessary in such cases to operate any state-of-the-art pressure (feed) rolls present on the wind-up turrets with a gap. The air drawn in between the individual layers at high machine speeds with this mode of operation is not removed. The contained air causes permanent local deformation of the web, a deformation conforming to the shape of the air cushion, under the pressure applied by the web. If contained air is present over a large area, lateral displacement of the roll is inventive. The quality of the web is greatly impaired in both instances. For example, it is absolutely necessary for pressure-sensitive chemically reactive carbon papers to have smooth, flat sheets of paper in which the microcapsules contained in certain coatings are undamaged.
The same problems occur, however, not alone with paper webs of widely varying nature, but also for example in the rolling up of thin sheets of readily deformable plastic.
(b) Description of the Prior Art
It has in the past been possible to master this problem to a certain extent only by greatly reducing the external diameter of the rolls. Rolls of greater external diameter are nevertheless required in order to achieve longer machine operation periods without roll replacement by means of greater web lengths.
DT-OS No. 24 39 212 discloses a device and a process for improvement in the quality of winding in the case of paper rolls with a large external diameter. Winding of the roll under tension results in compression of the paper leading to reduction of the thickness of the paper. The difference in thickness between the arriving weblike material and the average thickness of the wound layers is determined and is employed as a reference quantity for control of the winding mechanism. This device makes it possible to wind light-weight coated papers (LWC papers), in particular, into hard rolls of great external diameter without causing breaks in the web. This process is not, however, suitable for pressure-sensitive web materials such as papers with coatings containing pressure-sensitive microcapsules, since such materials must be wound in such a way that the web is not measurably compressed by the winding.
DE-OS No. 25 41 945 as well discloses a method of regulating the contact pressure of a contact roller. In the case of this automatic control the contact pressure is used among other things as a control factor and an attempt is made to solve the problem by means of expensive electronic equipment.
DE-AS No. 21 01 032 discloses a device by means of which dual layer sheet material can be separated and wound up separately.
The web of material is guided over a smoothing roller to the appropriate wind-up roller. This smoothing roller is applied to the wind-up roller under pressure of the lowest possible value so that any air between adjacent web layers inside the winding is removed. The smoothing roller is mounted so as to be rotatable about a swivel axis so that the pressure applied to the two sides can be independently adjusted in order to equalize slightly different roll diameters on the two sides of the wind-up roll. Pivoting movements of the wind-up roll in keeping with the increasing roll diameter are initiated mechanically by way of special elements mounted on the pivoting axis, ones which operate in conjunction with pins mounted on the support arms of the smoothing roller.